This invention relates to a novel apparatus for manufacturing solid-solder-deposit printed circuit boards by melting solder powder via induction heating consequently forming relatively thick layers of solid solder over the soldering pads of bare printed circuit boards.
The manufacturing of most modern electronic products requires a printed circuit board (PCB) that allows to electrically interconnect a variety of electronic components and also holds them together in a relatively rigid condition.
Manufacturing electronic products around PCBs requires a few sequential steps performed by different machines at the assembly floor. For example, such steps may comprise: (1) printing the PCB with soldering paste (an operation generally performed by stencil printing equipment), (2) placing surface-mount electronic components on that PCB face (an operation generally performed by an automated computer-controlled xe2x80x9cpick-and-placexe2x80x9d machine or by any other type of component placement equipment), (3) soldering the assembly (an operation generally performed inside a reflow oven), (4) cleaning the completed assembly (an operation that may involve washing and drying) and (5) testing the assembly for proper functionality (detects components damaged during step (3) and the presence of defective soldered joints.) Rework or rejection may be required after operation (5).
Deposition of solder paste on the PCB""s soldering pads (step (1) above) is nowadays accepted as the critical process step for controlling the quality of finished solder joints. Some statistical data shows that up to 64% of soldered joints defects can be traced back to the step of solder paste printing. The problem is almost intolerable when trying to solder high-pin-count surface-mount components which lead-pitch is smaller than 0.5 millimeter.
Repair to fix defective joints adds cost, may by itself create scrap, and invariably degrades the quality and reliability of the PCB assembly.
Consequently, if the traditional paste printing step is eliminated from the assembly floor, while still adequately delivering or interposing sufficient solder onto the joints to be soldered, many advantages will be derived.
Solid Solder Deposit (SSD) refers to a relatively thick layer of solid solder metallurgically bonded over the soldering pads of a bare-PCB. Bare-PCB refers to a conventional PCB that requires deposition of solder paste prior to a reflow soldering operation.
SSD printed circuit board (SSD-PCB) refers to a PCB with soldering pads covered by SSDs. Therefore, a SSD-PCB provides by itself the source of solder needed to solder components on it. The manufacture SSD-PCBs became more available to the United States electronics manufacturing or electronics packaging industry during 1998.
Because with SSD-PCBs no solder paste is used on the assembly floor, defect-free PCB assemblies are easily attained. SSD-PCBs can be optically and electrically inspected before accepted for components placement.
The most recent technology for producing SSD-PCBs is cover by the following four patents; (1) U.S. Pat. No. 5,315,070 Printed wiring board to which solder has been applied issued May 24, 1994, (2) U.S. Pat. No. 5,271,548 Method for applying solder to and mounting components on printed circuit boards issued Dec. 21, 1993, (3) U.S. Pat. No. 5,172,853 Method for applying solder to printed circuit boards and printed wiring board to which solder has been applied issued Dec. 22, 1993 and (4) U.S. Pat. No. 5,051,339 Method and apparatus for applying solder to printed wired boards by immersion issued Sep. 24, 1991.
When this inventor recognized that the prior art for manufacturing SSD-PCBs, including those disclose by the four above cited patents, need to be improved or replaced, the objectives and purposes of this invention were inspired, leading him to the conception and accomplishment of this invention.
The general objective of my invention is to provide the electronics manufacturing or electronics packaging industry with a new, safe, reliable, speedier, cheaper and useful apparatus and process for producing SSD-PCBs. Utilization of my invention will: (1) reduce the cost of SSD-PCBs, (2) improve SSD-PCBs quality and (3) require fewer manufacturing equipment. Also my invention allows to improve the quality and reliability of electronic products assembled around SSD-PCBs.
Further objectives and advantages of my invention will become apparent from a consideration of the drawings and following descriptions.